An inter-laboratory assessment of the thorium isotopic composition of synthetic and rock reference materials

We present a concerted international effort to cross-calibrate five synthetic Th isotope reference materials (UCSC Th A, OU Th U, WUN, IRMM-35 and IRMM-36), and six rock reference materials (UCSC TML, Icelandic ATHO, USGS BCR-2, USGS W-2, USGS BHVO-2, LV18) using multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). We then compare our new values with a compilation of literature mass spectrometric data for these reference materials and derive recommended consensus Th-230/Th-232 values for each. We also present isotope dilution U and Th concentration data for four rock reference materials (UCSC TML, Icelandic ATHO, USGS BCR-2, USGS W-2).